The present invention relates to a synchronizing circuit for a waveform observing apparatus such as an oscilloscope.
In conventional oscilloscopes, an observed signal is applied to a sync circuit for comparison with a triggering voltage level, and triggering pulses are generated at a timing when the observed signal exceeds the triggering voltage level thereby to display the desired still waveform of the observed signal.
When this technique is applied to digital signals or other complicated signals such as video signals it has become impossible to distinguish the periodic characteristics of the observed signal, so that it is difficult to obtain a desired observation as a result of a superposed display of waveforms with the same triggering voltage level but different periods one on another.
One of the conventional ways to obviate this inconvenience is to provide a band-pass filter which operates as a periodic signal extractor for a commercial video signal. However, use of such an extractor is troublesome and is not applicable for observation of other types of signals.